Hungarian emergency crews are working to dilute a toxic red sludge that has reached part of the Danube after it breached an industrial reservoir, killing at least four people.

The Hungarian national disaster unit said there had been no reports of dead fish in the Raba and Mosoni-Danube rivers reached by the spill, but all fish had died in the smaller Marcal river, which was contaminated first.

"Life in the Marcal river has been extinguished," said Tibor Dobson, a spokesman for the unit. "The main effort is now being concentrated on the Raba and the Danube. That's what has to be saved."

The spill's alkaline content in the Raba and Mosoni-Danube was around pH9 - the normal level is 6 to 8. Dobson said emergency teams were pouring plaster and acetic acid (vinegar) into the Raba-Danube meeting point to lower the pH value.

Gabor Figeczky, the Hungarian branch director of the WWF environmental group who visited the scene, said the impact on the Marcal had been worse than expected, but the level of alkaline should dilute to safe levels once the sludge reached the Danube, Europe's second longest river. "Based on our current estimates, it [the sludge] will remain contained in Hungary, and will reach Budapest with acceptable pH values," Figerczky told Reuters.

Path of the spill Graphic

Officials from downstream countries, which include Croatia, Serbia and Bulgaria, were testing the Danube every few hours, hoping that its huge volume would safely absorb the spill.

The reservoir burst at an alumina factory on Monday, disgorging a toxic torrent through three villages and creeks that flow into waterways connected to the Danube. Hungary's prime minister, Viktor Orban, visited Kolontar, the village closest to the spill. He declared one of the worst-hit areas uninhabitable, saying there was no point rebuilding there. "It is difficult to find the words. Had this happened at night everybody would be dead."

Local officials say 34 houses in the village of about 800 were too badly damaged to be refurbished. Soldiers, emergency workers and volunteers were trying to shovel out the mud yesterday, but the clean-up is expected to take months.

The prime minister suggested someone would be held accountable for the disaster. "This is so irresponsible that it is impossible to find words," he said.

Many people suffered from burns and eye ailments caused by corrosive elements in the mud. The flood, estimated at about 700,000 cubic metres (24m cubic feet), swept cars off roads and damaged bridges and houses. On Tuesday the government suspended production at the plant and police were investigating the disaster.

It is still not known why part of the reservoir collapsed and allowed the toxic torrent to sweep through the villages, killing at least four people and leaving three missing. Disaster officials said more than 150 people had been treated at hospitals, and 11 were still in serious condition.

MAL Zrt, the owner of the Ajkai Timfoldgyar alumina plant, said an inspection of the reservoir on Monday had shown nothing wrong. The reservoir was no longer leaking and a protective wall was being built around its damaged section.

Red sludge is a byproduct of the refining of bauxite into alumina, the basic material for manufacturing aluminum. Treated sludge is often stored in ponds where the water eventually evaporates.

Lajos Tolnay, chairman of MAL, said if the company stopped operating 3,000 jobs would be lost. But many people in Kolontar said they would not move back there as they did not trust the company.

"The whole settlement should be bulldozed into the ground," said resident Janos Potza. "There's no point for anyone to go back home."